1. Technical Field
The present invention relates generally to an improved image display system in which electromagnetic energy beams (e.g. collimated laser beams) are steered reflected within a or substantially planar structure in such a way which minimizes transmission intensity losses and the required number of energizing (e.g. laser beam) sources therewith. Also, the present invention relates to a novel method of fabricating such improved image display systems and devices in an inexpensive and mass-production manner.
2. Brief Description of the Prior Art
The need to produce images for visual display is widespread in our society. For decades, cathode ray tubes (CRT) have been used to scan electron (i.e. cathode ray) beams across phosphor display screens in order to form images in accordance with video signals. By virtue of physical necessity, such electron beams have been deflected within CRTs using magnetic and/or electric force fields which vary over time in accordance with video signals representative of images being sequentially displayed.
As an alternative to CRT display devices, it is possible to form images on a display surface by scanning a laser beam, rather than an electron beam, through a volume of space across a display surface. This approach is similar to that employed during conventional laser light shows, except that during a laser light show the display surface is typically a ceiling surface or atmospheric vapor. Scanning a laser beam across such a display surface may be accomplished using a variety of electro mechanical or electro-acoustic scanning technologies, numerous examples of which are described in great detail in xe2x80x9cLaser Scanning Notebookxe2x80x9d by Leo Beiser, published November 1992 by SPIE Optical Engineering Press, Bellingham, Washington, USA. However, like CRT display systems, conventional laser scanning display systems cannot be made physically compact nor can they avoid the use of galvanometric and electro-acoustic scanning apparatus. Such image display techniques suffer from a number of shortcomings and drawbacks. In particular, display structures embodying these techniques require a large volume of space due to the small angle through which the light beam can be deflected. Thus, if it is desired to scan a length B, the deflection arrangement must be positioned at a distance, A, providing an A/B ratio larger than 1, and therefore making it difficult, if not impossible to construct a flat-type display panel structure for color image display.
During the past few decades, a need has arisen for image display devices having both flat panel surface characteristics and thin depth dimensions. Numerous image display systems having such characteristics have been developed. In general, such systems have pixelated display surfaces which produce images composed of light rays emanating from discrete pixel elements activated in accordance with video signals. An electrical voltage is derived from the video signal for each pixel along the display surface, and the derived voltage is used to change either the optical or electrical properties of the associated pixel. In the case of LCD panels, such changes in optical properties of the pixels permit selective passage of light produced from behind the display surface. In the case of plasma display panels, changes in the electrical properties of encased plasma gases result in emission of light from activated pixels.
While these prior art display technologies have made it possible to make flat display devices with very thin depth dimensions and thus overcome the principal drawbacks associated with CRT display devices, prior art flat panel device technology has nevertheless suffered from some very significant shortcomings and drawbacks. In particular, it is presently impossible to make large-area flat panel display panels using current LCD technology. In addition, conventional flat panel display panels are very inefficient in terms of energy usage. Consequently, the uses to which conventional flat panel display technologies can be put have been necessarily limited.
In International PCT Publication Number WO 95/24671, based on the teachings of U.S. Pat. No. 5,459,591 to S. M. Faris, which is incorporated herein by reference in its entirety, Applicants addressed the above-described problems associated with prior art flat-panel display technology. This was done by teaching how to make large planar display structures comprising a plurality of imaging cells arranged in the form of an array, wherein each imaging cell incorporates a solid-state cholesteric liquid crystal (CLC) element, an electronically controlled, variable half-wave retarder and a source of circularly polarized light. The CLC element is disposed to an angle (45xc2x0) relative to the path along which light from the source is projected and is designed to reflect, at a given wavelength, one circular polarization of light and transmit the other. Using this characteristic, light of one polarization state or the other is presented to the variable retarder and depending on whether or not it is actuated, light is either diverted into another orthogonal path or remains in the original path. When another similar imaging cell is disposed in the orthogonal path, fight incident on that cell can also be diverted into yet another path or transmitted along the orthogonal path under control of a half-wave retarders associated with said another imaging cells. By selectively activating half-wave retarders associated with each of the cells, monochromatic or polychromatic light from a single source or multiple sources may be steered to a selected cell and reflected from its associated CLC element or elements. Utilizing successive cells in the array, and causing reflection of a modulated beam or beams, produces an image display frame akin to that produced by conventional television sets and viewable as an integrated picture. When successive image display frames are produced, moving images are displayed from the planar display structure.
While Applicants"" prior art image display system addresses many of the problems associated with prior art flat-panel display technologies, it nevertheless suffers from several shortcomings and drawbacks which have made widespread commercial applications thereof hitherto impractical.
In particular, within Applicants"" prior art flat panel display system design, the laser light beams sustain very high intensity losses during beam steering and transmission operations, making it very difficult to produce bright images without using high power laser light sources. In addition, within Applicants"" prior art flat panel display system design, numerous laser light sources are required, rendering the cost of manufacture prohibitive.
Thus, there is a great need in the art for an improved method and apparatus for steering electromagnetic beams within substantially planar display structures in order to produce color images therefrom, while avoiding the shortcomings and drawbacks of prior art apparatus and methodologies.
Accordingly, it is a primary object of the present invention to provide an improved flat panel display structure which overcomes the shortcomings and drawbacks of prior art systems and methodologies.
A further object of the present invention is to provide such a flat panel display structure, wherein a novel imaging array is employed that substantially reduces the transmission losses therewithin and the required number of energizing sources.
Another object of the present invention is to provide an imaging array which reduces transmission losses while simultaneously reducing the electromagnetic energy source requirement to one source.
Another object of the present invention is to provide an improved flat panel display structure which is capable of producing both 2-D and 3-D images in either the direct or projection viewing mode of operation.
Another object is to provide a novel method of fabricating a flat panel display structure in inexpensive and mass-production manner.
Another object of the present invention is to provide a novel and inexpensive method of manufacturing a flat panel display structure in a way which requires neither a vacuum envelope nor unacceptable high voltages.
Another object of the present invention is to provide such a flat panel display, wherein an array of CLC elements and controllable retarders are configured to scan a circularly polarized input bearm from point to point in a panel-like display, or to steer a circularly polarized input beam so that it can emanate from any location on an array of imaging.
Another object of the present invention is tot provide a flat-panel display structure having an A/B ratios which is very mush less than 1.
Another object of the present invention is to provide a flat-panel type scanning arrangement that enables scanning speeds in the microsecond range.
Another object of the present invention to provide a laser beam scanning array capable of scanning or steering an electromagnetic beam along a plurality of paths, without the use of electromechanical or electro-acoustic elements.
A further object of the present invention is to provide a one-dimensional (i.e. linear) laser beam scanning array, in which a collimated laser beam emanating from a single point source can be selectively steered along an one of a plurality of propagation paths in space so as to produce color images over large display surface areas.
A further object of the present invention is to provide such a laser beam scanning array wherein electronically controllable retarders, are used to change the paths of the collimated laser beam, instant-to-instant, while taking advantage of both the transmissive and reflective capabilities of CLC elements.
A further object of the present invention is to provide an electro-optical image display system having a substantially planar display panel with thin depth dimensions, and employing the novel laser beam steering array of the present invention.
A further object of the present invention is to provide such an electro-optical image display system for use in displaying images in either direct or projection viewing applications.
A further object of the present invention is to provide such an electro-optical image display system in which the need for vacuum envelopes, electron beam scanning, and backlighting type structures are altogether eliminated.
Another object of the present invention is to provide such an electro-optical display system, in which a laser beam having different spectral components in the visible band is steered within the image display device using an array of beam steering cells having the reflection-transmission characteristics of cholesteric liquid crystal (CLC) film material.
Another object of the present invention is to provide such an electro-optical image display system in which electronically controllable retarders and associated polarizing reflective elements are used to steer the laser beam, from point to point, within the flat panel image display device, on i a real-time basis, for video image display capabilities.
Another object of the present invention is to provide such an electro-optical image display system, in which the cross-sectional dimensions of the laser beam can be made sufficiently small so that the spatial period of the beam steering cells can also be made sufficiently small for high-resolution display surface applications, such as laptop computer systems and the like.
Another object of the present invention is to provide such an l electro-optical image display system, in which the laser beam is produced and intensity modulated external to the image display device and coupled thereto by way of a flexible fiber optical cable or like device.
Another object of the present invention to is provide such an electro-optical image display system, in which the display surface includes a pixelated panel of light dispersive pixels, each comprised of randomly dispersed microprisms or like elements, for dispersing the spectral components of the modulated laser beam as it emerges from the display surface in the direction of the viewer, thereby permitting full angular viewing of the displayed imagery.
Another object of the present invention is to, provide such an electro-optical image display system, in which the laser beam is shifted in wavelength as it emerges from the display surface of the system.
A further object of the present invention is to provide such an electro-optical image display system, in which the physical dimensions of the display surface can be made sufficiently large so as to permit direct public viewing of displayed imagery, as experienced in stadiums, theme parks, and other signage applications.
A further object of the present invention is to provide such an electro-optical image display system which can be readily adapted for viewing of stereoscopic images using either time-multiplexing, spatial-multiplexing, or spectral-multiplexing techniques well known in the art.
A further object of the present invention is to provide a novel method of steering collimated laser beams within an essentially flat panel structure, for laser beam scanning applications and image display applications alike.
Another object of the present invention is to provide an improved beam steering mechanism which can be used to construct various types of electro-optical systems and devices, including flat panel image display structures. The beam steering mechanism utilizes active and passive CLC elements arranged in branches to form a tree-like structure which shall be referred to hereinafter as xe2x80x9ca logic tree structurexe2x80x9d. Each branch of the logic tree structure comprises an active and passive CLC element. The active CLC element comprises a half-wave retarder and an electrode. Each succeeding branch of the logic tree structure contains twice as many branches as a preceding branch and, by activating the CLC element electrodes under control of a programmable pulsed source, inputs applied to the first stage of the logic tree structure are delivered as a scanned line of electromagnetic energy or light to the imaging cells of the last stage of the logic tree structure. By stacking identical logic tree structures with a laser source for each tree structure, a flat panel imaging array or display device can be formed in which the beam intensity losses are minimized during transmission therethrough.
Using a similar imaging array, transmission losses may be further reduced by using a logic tree structure having outputs which act as inputs to the imaging array, where formerly a plurality of lasers were required. By positioning an input logic tree structure perpendicularly to similar logic tree structures comprising the imaging array, a single source of energy (e.g. laser beam) provides an output at each of its imaging cells which acts as an input to an associated logic tree structure of the imaging array.
In this way, a scanned line is delivered from each imaging cell of the input logic tree structure to the first active element of an associated logic tree structure array. From there, under control of a programmable pulsed generator, portions of the scanned line are directed to the output imaging cells of each of the logic tree structure arrays. Two-dimensional images are built up in this way by activating the imaging cells of each logic tree structure array in succession.
Three dimensional images may be obtained using an approach similar to that just described by interleaving stereo displaced images from a 3-D camera at the output imaging cells of an imaging array by activating the first and every other logic tree structure of an array with one image and the second and every other logic tree structure with a stereo displaced image. Viewing glasses which respond to a different polarization for each eye are required to produce the 3-D effect. 2-D and 3-D images are provided by applying modulation to a laser from standard television cameras, as well as cameras designed to provide stereo-displaced images, respectively.
In the array which provides 3-D images, an image and a stereo displaced image are interleaved to provide the desired images each of which has a different circular polarization state.
The present invention also relates to a method of fabricating structures which provide the above described features. Since all the stages of a logic tree structure differ only in the number of branches they contain, the light beams, for example, applied from a laser beam could pass through a number of stages with minimum dispersion and maintain its original position even though relatively large structures are used to control its position. This permits the use of CLC elements, electrodes and half-wave retarder material which need not be divided into discrete elements in each logic tree structure. Thus, each CLC element, each electrode and each retarder material may extend from top-to-bottom or from side-to-side in each stage of an imaging array.
Stages of each logic tree structure can be fabricated by slicing layers of insulating material and CLC material at an angle of 45xc2x0. The thickness of the insulating material controls the spacing between the resulting CLC elements. Transparent layers, such as indium tin oxide are formed on both sides of the layer or layers containing spaced CLC elements. Using photolithographic techniques, one side in masked and etched to form an electrode over every other CLC element. A spacer element fixed to the periphery of each layer where the electrodes have been etched forms a volume into which half-wave retarder material is introduced in liquid form. The resulting stages are then stacked using as many as required to form an imaging array with a desired number of imaging cells. Stacking the stages, which are slices containing differently spaced CLC elements, automatically provides the logic tree structures which deliver scanned line to the output imaging cells. The method uses mass-production techniques and results in an inexpensive flat-panel display. In this way, stages containing two, four, eight, sixteen, CLC elements and so on have been mass produced. The stages are then stacked so that each stage contains twice as many CLC elements as a preceding stage, forming logic tree structures comprising the imaging cells which form an array.
These and other objects of the present invention will become apparent hereinafter and in the Claims to Invention.